Method of enhancing the efficacy and stability of ingredients in suspensions

ABSTRACT

A composition comprises a low-solubility ingredient having a particle size of at most 10 μm dispersed in a solvent. The ingredient is present in an amount greater than the saturation limit of the ingredient in the solvent. The composition passes the freeze-thaw cycling test.

BACKGROUND

Products intended for human or animal use, such as those regulated underthe U.S. Federal Food, Drug, and Cosmetic Act, often include acombination of ingredients that are classified by the U.S. Food and DrugAdministration (FDA) as monographed drugs (known as active ingredientsor “drug actives”) as well as ingredients that provide recognizedbeneficial effects but are not classified by the FDA as monographeddrugs (known as inactive ingredients or “claims actives”). Theseproducts are typically formulated as solutions to deliver effectiveamounts of the drug actives and claims actives to the target sites.

Formulating solutions can significantly complicate the manufacturingprocess since many drug actives and claims actives have poor or limitedsolubility in liquid delivery vehicles under ambient and human topicaluse temperatures. In addition, some drug actives and claims actives areonly soluble in solvents that are unsuitable for human topical use. Forexample, skin care ingredients such as antioxidants, skin soothingagents, skin brightening agents and vitamins are only soluble atmeaningful levels in solvents such as acetone, dichloromethane, dimethylsulfoxide and tetrahydrofuran.

Manufacturers can improve the solubility of drug actives and claimsactives in solvents by dissolving these ingredients at elevatedtemperatures to ensure complete dissolution. Solution preparation atelevated temperatures requires manufacturers to account for theconcentration limit of drug actives and claims actives in solution. Forexample, adding a claims active ingredient to an elevated temperaturesolution in an amount below its concentration limit at ambienttemperature may impose a concentration limit that is below the levelnecessary for efficacy, which will prevent the claims active fromproviding the desired effect in the final product. In addition, it iscommon for drug actives and claims actives to have a minimum effectiveconcentration that is above the ambient concentration limit. Thissituation requires manufacturers to formulate supersaturated solutionsto deliver an effective amount of the drug actives and claims actives.

Supersaturated solutions are problematic since they are unstable and mayexperience uncontrolled precipitation of the drug actives and claimsactives. The precipitation of ingredients often results in the formationof large, macroscopic crystals. Products containing visible crystals areaesthetically unacceptable to consumers and will reduce sales of thefinished products. Larger crystals are a significant problem becausethey can be felt by the consumer during application. Crystals largerthan 10 μm are perceived as grit by consumers, while crystals largerthan 100 μm are perceived as “glass shards” and can be highly irritatingwhen applied.

The precipitation of drug actives and claims actives is also problematicbecause it reduces the efficacy of the finished product. Larger crystalscan physically prevent ingredients in formulations from being deliveredto the target site. For example, in ultraviolet (UV) light protectiveformulations such as sunscreens, crystals that have precipitated out ofsolution will physically prevent the drug actives that provide UVprotection from being distributed to the skin. This results in aphenomenon known as “break through burn” and can cause erythema orsunburn at the areas of the skin without adequate UV protection.

A number of other conditions can result in precipitation of formulationingredients. Precipitation of ingredients can occur when aqueous-borneingredients in a formulation have poor solubility at physiological pHranges but enhanced solubility outside of physiological pH ranges. Inaddition, temperature fluctuations during storage and transport, such asfreeze-thaw conditions, can result in precipitation of ingredients informulations and large crystal formation.

Certain drug actives and claims actives are particularly susceptible toprecipitation out of formulations because their solubilities forcemanufacturers to form supersaturated solutions during their preparation.A well-known example of an ingredient that is prone to precipitate outof formulations is allantoin (also known as (2,5-dioxo-4-imidazolidinyl)urea, 5-ureidohydantoin or glyoxyldiureide), which is used in a widevariety of products for its skin conditioning, moisturizing, skinsoothing, wound healing, keratolytic, skin softening/smoothing,anti-inflammatory and anti-irritant properties (Igile, G. O. et al.,“Rapid method for the identification and quantification of allantoin inbody creams and lotions for regulatory activities”, InternationalJournal of Current Microbiology and Applied Sciences, Vol. 3, No. 7, pp.552-557 (2014)). The FDA has approved the use of allantoin as a skinprotectant when present in formulations in an amount of 0.5-2% (21 CFR347.10(a)). However, allantoin has a solubility limit of 0.5% in waterat 25° C., which prevents manufacturers from preparing formulationsincluding allantoin as a skin protectant across the full range ofconcentrations specified in the FDA monograph. The limited solubility ofallantoin forces manufacturers to choose between using less allantointhan allowed by the FDA or creating products that are prone to stabilityissues that can impair their efficacy.

Other ingredients that are known to experience precipitation issuesinclude quercetin, quercetin dihydrate, rutin, multifunctionalcurcuminoid additives and their derivatives (including curcumin,desmethoxycurcumin, bisdemethoxycurcumin andtetrahydrodiferuloyl-methane), phenol antioxidants (includingpolyphenols such as tannic acid, ellagic acid and raspberryellagitannin), flavonoids, isoflavonoids such as glabridin, flavanols(including catechins such as epigallocatechin gallate (EGCG)),dimethylmethoxy chromanol and carotenoids (including xanthophylls,astaxanthin, zeaxanthin and lutein).

SUMMARY

In a first aspect, the invention is a composition comprising alow-solubility ingredient having a particle size of at most 10 μmdispersed in a solvent. The ingredient is present in an amount greaterthan the saturation limit of the ingredient in the solvent. Thecomposition passes the freeze-thaw cycling test.

In a second aspect, the invention is a method of preparing a suspensioncomprising reducing the particle size of a low-solubility ingredient toat most 10 μm, and adding the ingredient to a solvent. The ingredient ispresent in an amount greater than the saturation limit of the ingredientin the solvent. The suspension passes the freeze-thaw cycling test.

In a third aspect, the invention is allantoin having an average particlesize of at most 10 μm.

Definitions

The term “particle size” means the average diameter of the particle asviewed by optical microscopy, electron microscopy or determined bystatic light scattering, unless otherwise stated. Particle size may beexpressed by number or by volume, or as a number weighted or volumeweighted distribution.

The term “low-solubility” means an ingredient that has a solubilitylimit of at most 2.0% in a given solvent at 25° C.

The term “suspension” means a composition that includes undissolvedparticles.

The “freeze-thaw cycling test” is a test of the stability of at leastone ingredient dispersed in a solvent. First, a test composition isprepared by adding the at least one ingredient to the solvent. Next, thetest composition is placed in a freezer at −20° C. After six hours thetest composition is removed from the freezer and allowed to return toroom temperature (25° C.). The test composition is then visuallyanalyzed by observation with the naked eye and by viewing a sample ofthe test composition using an optical microscope at 40×-200×magnification. The test composition is considered to pass thefreeze-thaw cycling test if no crystals are discernable by eye and ifthe test composition contains no particles larger than 10 microns (10μm) in at least one aspect when viewed under optical microscopy.

The “extended freeze-thaw cycling test” is a test of the stability of atleast one ingredient dispersed in a solvent. First, a test compositionis prepared by adding the at least one ingredient to the solvent. Next,the test composition is placed in a freezer at −20° C. After six hoursthe test composition is removed from the freezer and allowed to returnto room temperature (25° C.). The test composition is placed in thefreezer at −20° C. for six hours and allowed to return to roomtemperature an additional nine times. The test composition is thenvisually analyzed by observation with the naked eye and by viewing asample of the test composition using an optical microscope at 40×-200×magnification. The test composition is considered to pass the extendedfreeze-thaw cycling test if no crystals are discernable by eye and ifthe test composition contains no particles larger than 10 microns (10μm) in at least one aspect when viewed under optical microscopy.

The “shelf stability test” is a test of the long-term stability of acomposition containing at least one ingredient dispersed in a solvent.First, a test composition is prepared by adding the at least oneingredient to the solvent. Next, the test composition is placed in acontrolled environment at 25° C. After 18 months the test composition isremoved from the controlled environment. The test composition is thenvisually analyzed by observation with the naked eye and by viewing asample of the composition using an optical microscope at 40×-200×magnification. The test composition is considered to pass the shelfstability test if no crystals are discernable by eye and if the testcomposition contains no particles larger than 10 microns (10 μm) in atleast one aspect when viewed under optical microscopy.

The “skin feel test” is a test of the suitability of a compositioncontaining at least one ingredient dispersed in a solvent for topicaluse. First, a test composition is prepared by adding the at least oneingredient to the solvent. Next, the test composition is applied to theskin of a human tester. The test composition is considered to pass theskin feel test if the human tester does not perceive any solids or gritafter applying the test composition to his or her skin.

All percentages (%) are weight/weight percentages, unless statedotherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings and description.

FIG. 1 is a photograph of a 10.0 wt % allantoin suspension prepared byreducing the particle size of allantoin and a 10.0 wt % allantoinsolution prepared without reducing the particle size of allantoin.

FIG. 2 is a photograph of a 1.52 wt % allantoin suspension prepared byreducing the particle size of allantoin and a 1.52 wt % allantoinsolution prepared without reducing the particle size of allantoin.

FIG. 3 is a photograph of a 10.0 wt % allantoin suspension prepared byreducing the particle size of allantoin and a 10.0 wt % allantoinsolution prepared without reducing the particle size of allantoin afterone freeze-thaw cycle.

FIG. 4 is a photograph of a 1.52 wt % allantoin suspension prepared byreducing the particle size of allantoin and a 1.52 wt % allantoinsolution prepared without reducing the particle size of allantoin afterone freeze-thaw cycle.

FIG. 5 is an optical microscope image at 40× magnification of a 1.52 wt% allantoin solution prepared without reducing the particle size ofallantoin after one freeze-thaw cycle.

FIG. 6 is an optical microscope image at 200× magnification of a 1.52 wt% allantoin solution prepared without reducing the particle size ofallantoin after one freeze-thaw cycle.

FIG. 7 is an optical microscope image at 40× magnification of a 1.52 wt% allantoin suspension prepared by reducing the particle size ofallantoin after one freeze-thaw cycle.

FIG. 8 is an optical microscope image at 200× magnification of a 1.52 wt% allantoin suspension prepared by reducing the particle size ofallantoin after one freeze-thaw cycle.

FIG. 9 illustrates the number weighted particle size distribution of a20.0 wt % allantoin suspension in deionized water prepared by reducingthe particle size of allantoin in a 0.25 L media mill at 3000 RPM using0.3 mm diameter yttria-stabilized zirconia media.

FIG. 10 illustrates the volume weighted particle size distribution of a20.0 wt % allantoin suspension in deionized water prepared by reducingthe particle size of allantoin in a 0.25 L media mill at 3000 RPM using0.3 mm diameter yttria-stabilized zirconia media.

FIG. 11 illustrates the number weighted particle size distribution of a20.0 wt % allantoin suspension in C12-C15 alkyl benzoate prepared byreducing the particle size of allantoin in a 0.25 L media mill at 3000RPM using 0.3 mm diameter yttria-stabilized zirconia media.

FIG. 12 illustrates the number weighted particle size distribution of a20.0 wt % allantoin suspension in C12-C15 alkyl benzoate prepared byreducing the particle size of allantoin in a 0.25 L media mill at 3000RPM using 0.3 mm diameter yttria-stabilized zirconia media.

DETAILED DESCRIPTION

Manufacturers have attempted various changes to existing manufacturingprocesses to reduce or prevent the precipitation of drug actives andclaims actives from formulations. Modifications to the delivery systeminclude the use of porous delivery systems and liposomal deliverysystems. These modifications are typically costly and highly complex. Inaddition, the use of a different delivery system often still results informulations in which the drug actives and claims actives areconcentration limited

Manufacturers have also attempted to chemically modify formulationingredients to improve their stability. Chemical modifications to thedrug actives or claims actives include forming chemical derivatives ofthese ingredients. However, derivatization often compromises efficacy.For example, the functional groups available for derivatization inantioxidants are typically the same functional groups that impartefficacy, and the formation of multiple derivatives has been shown todrastically reduce or even eliminate the antioxidant power.

It has been recognized that low-solubility drug actives and claimsactives in suspensions exhibit crystal growth through Ostwald ripening.Ostwald ripening is a slow, thermodynamically-driven natural process inwhich small particles in solution dissolve and redeposit onto largerparticles. Ostwald ripening occurs spontaneously because large particlesare more thermodynamically stable than small particles since theinternal pressure in a particle is inversely proportional to its radius.This internal pressure difference results from molecules on the surfaceof a particle being less stable than the more well-ordered particles inthe interior of the particle. In addition, large particles have a lowersurface-to-volume ratio than smaller particles, which results in alower, and more stable, energy than small particles in a givendistribution. These properties cause smaller particles to dissolvefaster than larger particles, and the molecules to deposit from solutiononto the larger particles. Over time, the fraction of small particles insolution will decrease while the fraction of large particles in solutionincreases. Ostwald ripening is a well understood process and theparticle growth by Ostwald ripening can be calculated if sufficientvariables of the suspension are known (see, for example, van Westen, T.et al., “Effect of temperature cycling on Ostwald ripening”, CrystalGrowth & Design, Vol. 18, pp. 4952-4962 (2018)).

The present invention improves the stability of low-solubility drugactives and claims actives dispersed in a solvent by physicallymodifying these ingredients to reduce their particle size to at most 10μm. The particle size of drug actives and claims actives may be reducedusing common comminution methods to reduce the median particle size toat most 10 μm. This reduction in particle size results in ingredientswith a size below the threshold of what may perceived on human skin.Reducing the particle size of drug actives and claims actives allowsthese ingredients to be added to solutions in an amount greater than theamount necessary to saturate the solution. The improved stability may beachieved without the use of additional stabilizing ingredients, such assurfactants or emulsifiers.

Reducing the particle size of drug actives and claims actives insuspension improves their stability by discouraging large particlegrowth. Ingredients with a very small particle size provide a largenumber of nucleation sites or seeds for crystallization within asuspension containing the ingredients. Having many nucleation sitesallows many particles to grow a small amount rather than allowing fewerparticles grow a large amount and develop into larger crystals. Althoughthe ingredients may exhibit particle growth through Ostwald ripening, ithas been determined that the rate of formation of particles having amedian particle size larger than 10 μm through Ostwald ripening issignificantly greater than the typical shelf life of most consumerproducts containing ingredients in suspension.

Reducing the particle size of drug actives and claims actives insuspension also improves their bioavailability. Typically, ingredientsin the solid phase are not considered to be bioavailable. Reducing theparticle size of drug actives and claims actives to below 10 μmsignificantly increases the surface area of these ingredients. Theincreased surface area of drug actives and claims actives results inthese ingredients being bioavailable even when present in the solidphase.

Reducing the particle size of drug actives and claims actives alsoremoves limitations on how these ingredients may be added toformulations. Drug actives and claims actives with reduced particlesizes are present as suspended fine particles in solution, which allowstheir introduction in the solid phase. The presence of drug actives andclaims actives in the solid phase permits their addition to formulationphases in which these ingredients typically have limited solubility. Forexample, water-compatible ingredients may be added to the oil phase ofemulsions as well as lipophilic preparations and even anhydrouspreparations. Accordingly, the methods for improving the stability ofingredients in solution may be applied to any type of formulation.

A method of preparing a suspension includes reducing the particle sizeof a low-solubility ingredient to at most 10 μm and adding theingredient to a solvent in an amount greater than the saturation limitof the ingredient in the solvent. The ingredient may be added to thesolvent followed by reducing the particle size of the ingredient.Alternatively, the particle size of the ingredient may be reduced beforeadding the ingredient to the solvent.

The suspension may be prepared at ambient temperatures of 15-30° C.,including 16° C., 17° C., 18° C., 19° C., 20° C., 21° C., 22° C., 23°C., 24° C., 25° C., 26° C., 27° C., 28° C. and 29° C. Preferably, thesuspension is prepared at 25° C.

The low-solubility ingredient may be a drug active, a claims active, orcombinations thereof. Preferred ingredients include those having asolubility of at most 1.0% in the solvent at 25° C. More preferredingredients include those having a solubility of at most 0.5% in thesolvent at 25° C. Examples of low-solubility ingredients includeallantoin (solubility limit of 0.5% in water at 25° C.), quercetin (verypoorly soluble in neutral water), quercetin dihydrate (very poorlysoluble in neutral water), rutin (solubility limit of 0.013% in water at25° C.), multifunctional curcuminoid additives and their derivatives(including curcumin, desmethoxycurcumin, bisdemethoxycurcumin andtetrahydrodiferuloyl-methane), phenol antioxidants (includingpolyphenols such as tannic acid, ellagic acid and raspberryellagitannin), flavonoids, isoflavonoids such as glabridin, flavanols(including catechins such as epigallocatechin gallate (EGCG)),dimethylmethoxy chromanol, carotenoids (including xanthophylls,astaxanthin, zeaxanthin and lutein) and resveratrol (solubility of 0.03g/L in water).

The particle size of the ingredient may be reduced using any comminutionmethod that is capable of reducing the particle size to below 10 μm.Preferably, the comminution method is capable of reducing the particlesize to below 5 μm. More preferably, the comminution method is capableof reducing the particle size to below 3 μm. Most preferably, thecomminution method is capable of reducing the particle size to below 1μm. A preferred comminution method is milling. Examples of suitablemilling devices include vibratory mills, media mills, jet mills andhammer mills.

The comminution is preferably carried out in a liquid carrier that issuitable for use in human topical applications. The liquid carrier mayoptionally be the solvent. Examples of suitable liquid carriers includehumectants such as water, glycerin, propanediol and caprylyl glycol;hydrocarbons such as squalene, isodecane and polyisobutene; alcoholssuch as ethanol; glycerides such as triglycerides and capric/caprylictriglycerides; cosmetic fluids such as linear alkyl benzoates, C12-C15alkyl benzoate, ethylhexyl benzoate, isopropyl isostearate, jojobaesters, isoamyl laurate, octyldodecyl neopentanoate, butyloctylsalicylate, tridecyl salicylate and shea butter ethyl esters; vegetableoils and silicones. A preferred aqueous carrier is deionized water. Apreferred non-aqueous liquid carrier is C12-C15 alkyl benzoate.

The comminution parameters may be varied to produce a desired finalparticle size. Variable comminution parameters include the choice ofcomminution method, duration of comminution, acceleration (for vibratorymills), revolutions per minute (for media mills), type of media, size ofmedia and volume percent of media. Preferred media include 0.3 mm and0.5 mm diameter yttria-stabilized zirconia media.

The particle size of the ingredient may be reduced to 0.1-9.9 μm,including 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7μm, 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 9.6 μm, 9.7 μm and 9.8 μm.Preferably, the particle size is reduced to at most 5 μm, morepreferably the particle size is reduced to at most 3 μm, most preferablythe particle size is reduced to at most 1 μm.

A preferred ingredient with a reduced particle size is allantoin havingan average particle size of at most 10 μm. Allantoin may have an averageparticle size of 0.1-9.9 μm, including 0.1-5 μm, 0.1-3 μm and 0.5-3 μm.Preferably, the allantoin has an average particle size of at most 5 μm,at most 3 μm, at most 1 μm or at most 0.5 μm. A suspension may be formedby adding allantoin having an average particle size of at most 10 μm toa solvent.

The size of the particles may be determined using any suitable particlesize determination method. Examples of suitable particle sizedetermination include static light scattering, optical microscopy andelectron microscopy. Static light scattering may be used to determinethe number weighted and volume weighted particle size distributions.Optical microscopy may be used to estimate the particle size by volumeor number.

Drug actives and claims actives with reduced particle sizes may bepresent in compositions in an amount greater than the amount necessaryto saturate a solution containing these ingredients. This may bemeasured by reference to the solubility limit of the ingredient in agiven solvent. For example, drug actives and claims actives may bepresent in a composition at 2-1000 times their solubility limit,including 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100,200, 300, 400, 500, 600, 700, 800 or 900 times their solubility limit.

The suspension of drug actives and/or claims actives may be added to oneor more mixtures to create a formulation. The mixture may be a solution,a suspension or a colloid, such as an emulsion, sol, foam or gel. Thereduced particle size of the ingredients in suspension allows thesolution to be added to any mixture suitable for topical human or animaluse. For example, the suspension may be added to the continuous phase ofan oil-in-water emulsion, the continuous phase of a water-in-oilemulsion, lipophilic preparations or anhydrous preparations.

A composition may contain a low-solubility ingredient having a particlesize of at most 10 μm dispersed in a solvent. The ingredient may bepresent in an amount greater than the saturation limit of the ingredientin the solvent. The solvent may be any substance that is suitable fortopical human or animal use. Preferably, the solvent is apharmaceutically acceptable solvent. The ingredient may be a drugactive, a claims active or combinations thereof.

The stability of the composition may be evaluated by subjecting it toone or more tests that model the long-term stability of compositions.Preferably, the composition passes the freeze-thaw cycling test. Morepreferably, the composition passes the extended freeze-thaw cyclingtest. Preferably, the composition passes the shelf stability test. Thestability of the composition may also be evaluated by subjecting it toone or more tests developed by an independent organization, such as theInternational Council for Harmonisation of Technical Requirements forPharmaceuticals for Human Use (ICH). Preferably, the composition isstable under the ICH accelerated stability conditions.

The composition preferably is suitable for topical human or animal use.The composition may be evaluated to determine its suitability fortopical use by applying it to the skin of a human tester. Preferably,the composition passes the skin feel test.

The composition may be formulated for use in a variety of differentapplications. Examples of suitable formulations include medications(medicines and pharmaceuticals or drugs), baby products (lotions, oils,powders and creams), bath products (oils, tablets, salts, soaps,detergents and bubble baths), eye makeup (eyebrow pencils, eyeliners,eye shadow, eye lotions, eye makeup remover and mascara), fragranceproducts, hair care products (conditioners, hair sprays/fixatives,straighteners, permanent waves, rinses, shampoos and tonics),makeup/cosmetics (blushes, face powders, foundations, lipsticks, makeupbases and rouges), nail care products (cuticle softeners, creams andlotions), oral hygiene products (dentifrices/toothpastes, mouthwashesand breath fresheners), personal hygiene products (deodorants anddouches), shaving products (aftershaves and shaving cream), skin careproducts (skin cleansing creams, lotions, liquids and pads; face andneck creams, lotions, powders and sprays; body and hand creams, lotions,powders and sprays; foot powders and sprays; moisturizers; night creams,lotions, powders and sprays; paste masks/mud packs; and skinfresheners), sun exposure products (sunscreens; suntan gels, creams,liquids and sprays; indoor tanning preparations) and nutritionalsupplements (oils, suspensions and other liquids containing vitamins,minerals, proteins, amino acids, bodybuilding supplements, essentialfatty acids, natural products or probiotics; nutritional beverages;nutritional oil supplements). Preferred formulations include sunscreens,skin care products and nutritional/dietary supplements.

The composition may be provided in any form suitable for its intendedroute of administration. For example, a composition intended for topicalapplication may be provided as a topical suspension, lotion, cream,ointment, gel, hydrogel, foam, paste, tincture, liniment, sprayableliquid or aerosol.

The composition may be formulated for human or animal consumption. Aconsumable composition may contain ingredients such as nutritionalsupplements or food additives having a particle size of at most 10 μmdispersed in a solvent.

EXAMPLES Example 1—Comparative Test Between Comminuted AllantoinSuspensions and Aqueous Allantoin Solutions

A 10.0 wt % allantoin (DSM, (2,5-dioxo-4-imidazolidinyl)urea, CAS No.97-59-6) suspension was prepared in deionized water. The suspension wasmilled for 3 minutes on a vibratory mill at an acceleration of 100 Gusing 0.5 mm diameter yttria-stabilized zirconia media at 50 volumepercent. The suspension was examined under an optical microscope and theprimary particle size was estimated to be approximately 3 microns (3 μm)by volume and 1 micron (1 μm) by number.

A 1.52 wt % allantoin (DSM, (2,5-dioxo-4-imidazolidinyl)urea, CAS No.97-59-6) suspension was prepared in deionized water. The suspension wasmilled for 3 minutes on a vibratory mill at an acceleration of 100 Gusing 0.5 mm diameter yttria-stabilized zirconia media at 50 volumepercent. The suspension was examined under an optical microscope and theprimary particle size was estimated to be approximately 3 microns (3 μm)by volume and 1 micron (1 μm) by number.

Comparative solutions were prepared at 10.0 wt % and 1.52 wt % allantoinin deionized water. The comparative solutions were heated to 80° C.under light mixing for approximately 15 minutes. A manufacturer'stechnical data sheet indicated that stable solutions may be prepared atthis temperature with no decomposition. The 1.52 wt % solution achievedcomplete dissolution, while the 10.0 wt % solution achieved nearlycomplete dissolution.

Visual Analysis

Photographs of the samples were taken. FIG. 1 is a photograph of the10.0 wt % allantoin suspension and solution. FIG. 2 is a photograph ofthe 1.52 wt % allantoin suspension and solution. As may be seen in FIGS.1 and 2, the milled suspensions appeared opaque and the solutionsappeared transparent.

Freeze-Thaw Warm Test

The samples were tested for freeze-thaw stability and behavior. Thesuspensions and solutions were placed in a freezer at −20° C. for 6hours and subsequently returned to room temperature. Photographs of thesamples were taken. FIG. 3 is a photograph of the 10.0 wt % allantoinsuspension and solution after one freeze-thaw cycle. FIG. 4 is aphotograph of the 1.52 wt % allantoin suspension and solution after onefreeze-thaw cycle.

The allantoin suspensions remained homogenous after one freeze-thawcycle and showed no evidence of visible precipitates. By contrast, theallantoin solutions showed a large fraction of precipitation andincluded significant large crystals that settled out of solution. Thecrystals were discernable by eye, which indicates that the crystals werelikely larger than 30 microns (30 μm). These results were exhibited atboth concentrations for the suspensions and the solutions.

The 1.52 wt % allantoin samples were then examined using opticalmicroscopy. FIG. 5 is an optical microscope image at 40× magnificationof the 1.52 wt % allantoin solution after one freeze-thaw cycle. FIG. 6illustrates an optical microscope image at 200× magnification of the1.52 wt % allantoin solution after one freeze-thaw cycle. FIG. 5 andFIG. 6 both show large crystals. Most of the precipitated crystals werelarger than 10 microns (10 μm) in at least one aspect. A substantialnumber of crystals were larger than 30 microns (30 μm) in at least oneaspect. Some particles exceeded the field size at some magnifications,which indicated that these crystals were larger than 100 microns (100μm) in at least one aspect.

FIG. 7 illustrates an optical microscope image at 40× magnification ofthe 1.52 wt % allantoin suspension after one freeze-thaw cycle. FIG. 8illustrates an optical microscope image at 200× magnification of the1.52 wt % allantoin suspension after one freeze-thaw cycle. FIG. 7 andFIG. 8 show that no large particles were formed as a result of thefreeze-thaw cycle. In addition, no discernable particle growth wasobserved at either magnification. The lack of particle growth indicatedthat the primary particle size was approximately 3 microns (3 μm) byvolume and less than 1 micron (1 μm) by number. The upper limit of theparticle size by volume was confirmed to be less than 4 microns (4 μm)by drawing the suspension down on a Hegman grind gauge.

Skin Feel Test

The allantoin suspensions were tested for skin feel. The 1.52 wt %suspension and the 10.0 wt % suspension were applied to the skin afterone freeze-thaw cycle. Neither suspension developed crystals ofsufficient size to be discerned in a skin feel test. These results wereconsistent with the particle size determined by optical microscopy. Theskin feel test indicated that that the allantoin suspensions were bothsuitable for cosmetic preparations.

Loss on Drying Test

Two 1.52 wt % allantoin solutions were tested for loss on drying (LOD)at 105° C. after one freeze-thaw cycle and returning to 25° C. The LODof the clear supernatant indicated an allantoin concentration of0.25-0.35%. This concentration range was consistent with the initialsolubility from the thawing cycle. The concentration was predicted toreturn to the concentration limit of 0.5% at 25° C. over time. However,the rate of dissolution was predicted to be depressed since theprecipitation fraction included large crystals with a low surface area.

Example 2—Repeated Freeze-Thaw Cycling Test for Comminuted AllantoinSuspension

The 1.52 wt % allantoin comminuted suspension described in Example 1 wassubject to nine additional freeze-thaw cycles (a total of 10 freeze-thawcycles). The suspension was then examined using optical microscopy. Nodiscernable particle size growth was observed.

These results indicate that solutions containing an ingredient having areduced particle size and present at a level above its solubility limitin the solvent are highly stable, and that this high stability can beachieved without the use of stabilizing ingredients.

Example 3—Preparation of 20% Aqueous Allantoin Concentrate Suspension

A 20.0 wt % allantoin (DSM, (2,5-dioxo-4-imidazolidinyl)urea, CAS No.97-59-6) suspension was prepared in deionized water. The suspension wasmilled in a 0.25 L media mill at 3000 RPM using 0.3 mm diameteryttria-stabilized zirconia media. The particle size distribution of theresultant suspension showed a number weighted mean particle size of0.167 microns (0.167 μm) and a volume weighted mean particle size of 3.9microns (3.9 μm) as measured by static light scattering using a HORIBA®LA-960 laser particle size analyzer. FIG. 9 illustrates the numberweighted particle size distribution. FIG. 10 illustrates the volumeweighted particle size distribution. Optical microscopy analysis of thesuspension indicated a particle size consistent with the comminutedallantoin suspensions described in Example 1.

The 20.0 wt % allantoin suspension was added to the continuous phase ofan oil-in-water sunscreen emulsion at a concentration of 0.7% in thewater phase. The resulting formulation was shown to be stable under theInternational Council for Harmonisation of Technical Requirements forPharmaceuticals for Human Use (ICH) accelerated stability conditions.

These results indicate that aqueous suspensions can contain allantoin atconcentrations significantly above its solubility limit when theparticle size of allantoin has been reduced to below 10 μm. In addition,the high-concentration suspensions demonstrate high stability insolution.

Example 4—Preparation of 20% Non-Aqueous Allantoin ConcentrateSuspension

A 20.0 wt % allantoin (DSM, (2,5-dioxo-4-imidazolidinyl)urea, CAS No.97-59-6) suspension was prepared in C12-C15 alkyl benzoate (FINSOLV® TN,Innospec). The suspension was milled in a 0.25 L media mill at 3000 RPMusing 0.3 mm diameter yttria-stabilized zirconia media. The particlesize distribution of the resultant suspension showed a number weightedmean particle size of 0.195 microns (0.195 μm) and a volume weightedmean particle size of 3.0 microns (3.0 μm) as measured by static lightscattering using a HORIBA® LA-960 laser particle size analyzer. FIG. 11illustrates the number weighted particle size distribution. FIG. 12illustrates the volume weighted particle size distribution. Opticalmicroscopy analysis of the suspension indicated a particle sizeconsistent with the comminuted allantoin suspensions described inExample 1.

The 20.0 wt % allantoin suspension was added to the continuous phase ofa water-in-oil sunscreen emulsion at a concentration of 0.7% in thewater phase. The resulting formulation was shown to be stable under theInternational Council for Harmonisation of Technical Requirements forPharmaceuticals for Human Use (ICH) accelerated stability conditions.

These results indicate that non-aqueous suspensions can containallantoin at concentrations significantly above its solubility limitwhen the particle size of allantoin has been reduced to below 10 μm. Inaddition, the high-concentration suspensions demonstrate high stabilityin solution.

Example 5—Bioavailability Study

A comminuted suspension of allantoin in deionized water and acomparative solution of allantoin in deionized water (not comminuted)were prepared as described in Example 1. Sunscreens were then preparedcontaining the comminuted allantoin suspension and zinc oxide, andcontaining the allantoin solution and zinc oxide.

A human subject applied each sunscreen to separate areas of their skin.Their skin was then exposed to ultraviolet light. The area of skin thatreceived the sunscreen with the comminuted allantoin suspensionexhibited less erythema (redness) than the area of skin that receivedthe sunscreen containing the allantoin solution. These results indicatethat reducing the particle size of the allantoin by comminutionincreased the bioavailability of the allantoin.

REFERENCES

-   1. Igile, G. O. et al., “Rapid method for the identification and    quantification of allantoin in body creams and lotions for    regulatory activities”, International Journal of Current    Microbiology and Applied Sciences, Vol. 3, No. 7, pp. 552-557    (2014).-   2. Becker, L. C. et al., “Final report of the safety assessment of    allantoin and its related complexes”, International Journal of    Toxicology, Vol. 29, Supplement 2, pp. 84S-97S (2010).-   3. van Westen, T. et al., “Effect of temperature cycling on Ostwald    ripening”, Crystal Growth & Design, Vol. 18, pp. 4952-4962 (2018).

1. A composition, comprising a low-solubility ingredient having aparticle size of at most 10 μm dispersed in a solvent, wherein theingredient is present in an amount greater than the saturation limit ofthe ingredient in the solvent, and the composition passes thefreeze-thaw cycling test.
 2. The composition of claim 1, wherein thecomposition passes the extended freeze-thaw cycling test.
 3. Thecomposition of claim 1, wherein the composition passes the skin feeltest.
 4. The composition of claim 1, wherein the ingredient is selectedfrom the group consisting of drug actives, claims actives andcombinations thereof.
 5. The composition of claim 1, wherein theingredient has a particle size of at most 5 μm by volume and at most 1μm by number as determined by optical microscopy. 6-7. (canceled)
 8. Thecomposition of claim 1, wherein the ingredient comprises at least onesubstance selected from the group consisting of allantoin, quercetin,quercetin dihydrate, rutin, multifunctional curcuminoid additives andtheir derivatives, curcumin, desmethoxycurcumin, bisdemethoxycurcumin,tetrahydrodiferuloyl-methane, phenol antioxidants, tannic acid, ellagicacid, raspberry ellagitannin, flavonoids, isoflavonoids, glabridin,flavanols, catechins, epigallocatechin gallate (EGCG), dimethylmethoxychromanol, carotenoids, xanthophylls, astaxanthin, zeaxanthin, lutein,and resveratrol.
 9. (canceled)
 10. The composition of claim 1, whereinthe solvent is selected from the group consisting of water, humectants,hydrocarbons, alcohols, glycerides, cosmetic fluids, vegetable oils, andsilicones.
 11. The composition of claim 1, wherein the composition isformulated as a topical solution, lotion, cream, ointment, gel,hydrogel, foam, paste, tincture, liniment, sprayable liquid or aerosol.12. The composition of claim 1, wherein the composition comprises aformulation selected from the group consisting of medications, babyproducts, bath products, eye makeup, fragrance products, hair careproducts, makeup/cosmetics, nail care products, oral hygiene products,personal hygiene products, shaving products, skin care products, sunexposure products and nutritional supplements.
 13. The composition ofclaim 1, wherein the composition comprises a sunscreen.
 14. Thecomposition of claim 1, wherein the composition comprises a skin careproduct.
 15. The composition of claim 1, wherein the ingredientcomprises a nutritional supplement or a food additive.
 16. (canceled)17. A method of preparing a suspension, comprising: reducing theparticle size of a low-solubility ingredient to at most 10 μm; andadding the ingredient to a solvent; wherein the ingredient is present inan amount greater than the saturation limit of the ingredient in thesolvent, and the suspension passes the freeze-thaw cycling test.
 18. Themethod of claim 17, wherein the suspension is prepared at 15-30° C. 19.The method of claim 17, wherein the ingredient is selected from thegroup consisting of drug actives, claims actives and combinationsthereof.
 20. The method of claim 17, wherein the reducing comprisesreducing the particle size of an ingredient to at most 5 μm. 21-22.(canceled)
 23. The method of claim 17, wherein the ingredient comprisesat least one substance selected from the group consisting of allantoin,quercetin, quercetin dihydrate, rutin, multifunctional curcuminoidadditives and their derivatives, curcumin, desmethoxycurcumin,bisdemethoxycurcumin, tetrahydrodiferuloyl-methane, phenol antioxidants,tannic acid, ellagic acid, raspberry ellagitannin, flavonoids,isoflavonoids, glabridin, flavanols, catechins, epigallocatechin gallate(EGCG), dimethylmethoxy chromanol, carotenoids, xanthophylls,astaxanthin, zeaxanthin, lutein, and resveratrol.
 24. (canceled)
 25. Themethod of claim 17, wherein the reducing comprises milling. 26.(canceled)
 27. The method of claim 17, wherein the solvent is selectedfrom the group consisting of water, alcohols, triglycerides, linearalkyl benzoates, vegetable oils, and silicone oils.
 28. The method ofclaim 17, wherein the suspension is not supersaturated. 29-42.(canceled)